The present invention relates to the art of multi-axis direction and motion encoding. It finds particular application in conjunction with operator manipulation of portions of video displays relative to three axes and will be described with particular reference thereto. For example, the encoder may be used to shift a cursor or portions of a video display along the tube, vertically, longitudinally, or rotationally, i.e. a three axis manipulation. Such manipulations may be performed to move, align, or otherwise position medical diagnostic images. The invention is also applicable to cursor manipulation for home computer terminals, video games, CAD/CAM systems, and the like.
Heretofore, two and three dimensional trackballs have been readily available. Typically, a two dimensional track ball was supported on two perpendicular rollers. Frictional engagement between the ball and the rollers caused rotation of the ball to be translated into corresponding rotation of each roller. More specifically, the rotation of each roller was indicative of rotation of the ball relative to an axis parallel to the central axis of the roller. Encoders were connected with each roller to convert the rotation of the corresponding roller into electrical signals, e.g. an electrical pulse signal for each increment of a rotation.
For a three axis trackball, a third roller was positioned in frictional engagement with the ball. Normally, the three rollers were positioned with their central axes parallel to orthogonal coordinates. More specifically, one roller was normally positioned to measure left and right rotational movement of the ball, another roller for forward and aft rotation of the ball, and the third axis was positioned to measure rotation of the ball about a vertical axis. To rotate the ball and encode about the first two axes, one can normally palm the ball and merely push in the desired direction. To encode movement about the vertical axis, one must normally grab the ball with the fingers and twist.
One of the problems with the prior art three axis balls, particularly smaller diameter balls, resided in the difficulty to encode movement around the third or vertical axis. Most operators lacked sufficient fine motor skills and coordination to rotate the ball about the vertical axis without also causing translating motion about one or both of the horizontal axes. By way of example, most operators could not rotate a displayed cursor without also shifting its origin.
The present invention contemplates a new and improved track ball type arrangement which enables precise orientation or rotation relative to a third axis without altering the first and second axis.